Field of the Invention
The present invention relates to a variable nozzle unit capable of making variable a passage area for (or a flow rate of) an exhaust gas to be supplied to a turbine impeller side in a variable geometry system turbocharger. The present invention also relates to a variable geometry system turbocharger.
Description of the Related Art
In recent years, various developments have been made with regard to a variable nozzle unit to be installed in a variable geometry system turbocharger. Japanese Patent Application Publications Nos. 2009-243300 and 2009-243431 disclose variable nozzle units of the related art. An essential configuration of the variable nozzle units is as follows.
In a turbine housing of a variable geometry system turbocharger, base rings are disposed concentrically with a turbine impeller. Each base ring is provided with multiple support holes formed in a penetrating manner. The support holes are arranged at equal intervals in a circumferential direction of the base ring. The base rings are also provided with multiple variable nozzles which are disposed to surround the turbine impeller at equal intervals in the circumferential direction of the base rings. Each variable nozzle rotates in a forward direction or a reverse direction (in an opening direction or a closing direction) about its pivot which is parallel to a pivot of the turbine impeller. Further, a nozzle shaft is integrally formed on a side surface of each variable nozzle, the side surface being located on one side in an axial direction of the turbine impeller. Each nozzle shaft is rotatably supported by a corresponding support hole provided in one of the base rings.
A guide ring is provided on one side, in the aforementioned axial direction, of the base rings. The guide ring is provided concentrically with the turbine impeller. Multiple support claws are formed radially on an outer peripheral edge of the guide ring at intervals in its circumferential direction. The multiple support claws support a drive ring rotatably in the forward direction and the reverse direction about the pivot of the turbine impeller. Here, the drive ring rotates in the forward direction or the reverse direction by the drive of a rotary actuator. The drive ring is provided with engagement portions which are as many as the variable nozzles. The engagement portions are arranged at equal intervals in the circumferential direction. In addition, a synchronous link member (a nozzle link member) is integrally connected to the nozzle shaft of each variable nozzle. A tip end of each synchronous link member is engaged with the corresponding engagement portion of the drive ring.
When the drive ring rotates in the forward direction, the multiple synchronous link members swing in the forward direction, whereby the multiple variable nozzles synchronously rotate in the forward direction (the opening direction). This increases the area of a passage for an exhaust gas to be supplied to the turbine impeller side. On the other hand, when the drive ring rotates in the reverse direction, the multiple synchronous link members swing in the reverse direction, whereby the multiple variable nozzles synchronously rotate in the reverse direction (the closing direction). This reduces the area of the passage for the exhaust gas.
As described above, the variable nozzle unit of the related art requires the guide ring, the drive ring, and the multiple synchronous link members as the configuration to rotate the multiple variable nozzles synchronously in the forward direction or the reverse direction. For this reason, the number of components of the variable nozzle unit increases and the configuration of the variable nozzle unit is complicated. In addition, the increase in the number of components leads to an increase in manufacturing costs of the variable nozzle unit, in other words, complication in a configuration of a variable geometry system turbocharger and an increase in manufacturing costs of the variable geometry system turbocharger.